The study, termed “An Analysis of Climate Engineering as a Response to Climate Change”, calculates that proposals for a fleet of 1,900 unmanned ships capable of spraying water into the air to seed clouds would cost just $9 billion. The clouds would then reflect one to two per cent of the sun’s energy back into space, effectively cancelling out the warming effect generated by the past century’s carbon emissions.

After exploring other geoengineering options, the study concluded that the cloud ship fleet offered the most cost-effective option, providing $2,000 worth of benefits for each $1 invested. In contrast, it calculated that releasing aerosol particles into the atmosphere would cost $230bn over 25 years and would deliver $15 of benefits for each dollar invested, while space mirrors and carbon capture systems were deemed less attractive still from both a technical and a cost perspective.

However, green groups were quick to downplay the proposals, arguing that geo-engineering projects are unlikely to prove effective and could distract from efforts to cut carbon emissions.